1. Field of the Invention
The present invention relates to a slide-type cervical plate and more particularly to an anti-backout device with which said cervical plate is equipped and which is intended to hold the bone anchor screws in position.
2. Description of the Related Art
U.S. Pat. No. 5,876,402 discloses a locking device comprising a screw and a plate which are intended to immobilize bones by fixation thereinto, notably into the vertebral bodies of a spinal column.
The plate has through-holes with a conically tapered profile into which are respectively introduced a fixation screw with a spherical head and a conical coupling element which fits around the screw head and presses against the conical edges of the hole.
Each through-hole in its upper part and above the conical coupling element has a coaxial slot intended to accept a locking element formed of a split annular clamp. The split clamp is centered about the axis of the conically profiled hole, preventing any backing-out of the conical coupling element.
U.S. Pat. No. 5,879,389 discloses a knee prosthesis the tibial plate of which is fixed into the bone using anchor screws housed in holes that pass through said plate. The upper bore of the hole that accommodates the head of each screw has a coaxial slot intended to accommodate a split annular clamp preventing screw backout.
Also, European patent EP 1 185 210 discloses an orthopedic implant comprising an anti-backout device comprising:                at least one housing which is axially offset with respect to the main axes XX′ and YY′ of the bore,        and at least one retaining means which collaborates with the corresponding housing so that said retaining means partially crosses the corresponding bore accepting the fixator screw so as to be able to deform elastically under a pressing load so as to allow the screw to pass and be fitted into its bore, whereas the retaining means reverts to a non-deformed original position when the pressing load ceases to be applied, so that it comes into position over the head of the screw so as to prevent the latter from moving with respect to the implant in a direction parallel to the longitudinal axis of the bore.        